Two improved invisibility devices show themselves
— -- Harry Potter's cloak it isn't, but scientists report the creation of two visible-light "invisibility cloak" prototypes that promise improved optics and cellphones and, yes, invisibility.
The microscopic devices aren't actually in a cloak at this point, but they do bend light around their surfaces, researchers headed by Xiang Zhang of the University of California-Berkeley say. The devices rely on metamaterials, specially structured materials that in these cases have surfaces dotted with holes smaller than the width of visible light waves, less than 0.00003 of an inch across, which smoothly shuttle light rays around them.
"Being able to bend light in unusual ways is important for applications that almost resemble magic," physicist Ulf Leonhardt of Scotland's University of St. Andrews, who was not part of the prototype teams, writes in an e-mail. "There still is a long way to go, but the Berkeley team made an important step."
The field has been a hot area of study. Invisibility devices up till now have involved metamaterial devices that were "invisible" only from one angle or to microwaves but not visible light.
One of the new prototypes is a woven fishnet of silver nanowires, each one about 10,000 times thinner than a human hair. It was reported this week in the journal Science.
The team tested the device for red, or visible, light and infrared light and said the prototype bends red light from all angles hundreds of times more effectively than in past attempts.
The other device, reported this week in Nature magazine, relies on 21 stacked grids of silver and magnesium fluoride of similarly small sizes. The researchers found that the device bent infrared light around the grids.
Applications for invisibility devices extend beyond shielding oneself for an escape from a wizards academy. Shielding lenses from unwanted light frequencies would improve camera function, for example, and antennas invisible to noisy electromagnetic waves would fine-tune cellphone and radio communications.
